At present, various kinds of electrical elements are inserted into the ends of catheters for various medical purposes. The signals from these elements are transmitted to various devices by means of electrical wires arranged in the catheter body and in extension tubes which are connected to it.
In order to insert these catheters easily into the body, they are usually made of a relatively flexible material such as soft plastic, and they can be easily stretched by an external stress or the action of heat. The electrical wires, on the other hand, generally consist of metallic material, and they are capable of much less elongation than the catheter body by an external stress or heat. When the catheter is carelessly stretched during handling, therefore, these wires easily break.
Various methods have been proposed in the prior art to prevent the breaking of electrical wires in such catheters. Such methods include, for example, increasing the outer diameter of the wires to thereby increase their breaking strength; adding additives to the materials of the wires to thereby increase their breaking strength; or coiling the wires throughout the catheter body and the whole of the extension tubes.
However, the technique of increasing the outer diameter of the wires cannot be applied to catheters of a small diameter. The addition of additives to wires does not provide sufficient strength for catheters of a small outer diameter, and is also undesirable as it increases the electrical resistance which interferes with signal transmission performance. Coiling the wires throughout the whole length of the catheter is practically impossible if the internal cavity is narrow, or the catheter is too long.